This invention relates to piezoelectric vibrator units having holder means holding a vibrator plate or plates.
FIGS. 1a and 1b show a piezoelectric vibrator unit of prior art having a vibrator plate 1 mounted on a base support 8 by means of electrically conductive supporting arms 4 and 5. Vibrator plate 1 may be of quartz, lithium tantalate, lithium niobate, or piezoelectric ceramics, and has a pair of excitation electrodes which are formed on the central portions of said vibrator plate at opposite sides thereof. Supporting arms 4 and 5 which support vibrator plate 1 by means of notches 6 and 7 and a binding agent are fixed to lead wires 9 and 10. Accordingly, excitation electrodes 2 and 3 are connected respectively electrically through the leads extending to the periphery of the plate 1, to lead wires 9 and 10.
In the manufacture of such a piezoelectric vibrator unit of prior art, vibrator plate 1 is subjected, prior to being mounted on base support 8, to vacuum evaporation processes to form excitation electrodes 2 and 3 by using a masking means. Subsequently, vibrator plate 1 is mounted as shown in FIGS. 1a and 1b, and is subjected to a secondary vacuum evaporation process so as to form a vacuum evaporated film on one of said excitation electrodes so that the vibrator plate can be vibrated at a desired vibration frequency.
And, in such a secondary vacuum evaporation process for the microadjustment of the vibration frequency, the vacuum evaporated film must be formed correctly on an excitation electrode formed by a vacuum evaporation process which has been effected previously. Otherwise, generation of spurious changes in dynamic capacitance and dynamic inductance of the plate will be caused.
Furthermore, in a piezoelectric vibrator unit of prior art as mentioned in the foregoing, due to weakness of supporting means such as supporting arms 4 and 5 as compared with the weight of the vibrator plate, the excitation electrodes which have been formed in said prior vacuum evaporation are apt to be dislocated from predetermined positions for the mask which are to be subjected to said secondary vacuum evaporation through said mask. And, it will readily be seen that the alignment of positions for the secondary vacuum evaporation is very troublesome.
Another piezoelectric vibrator unit having two vibrator plates of prior art is shown in FIGS. 2a and 2b. In the figures, 11 and 12 are respectively a piezoelectric vibrator plate such as indicated at 1 in FIGS. 1a and 1b. 13 and 14, and, 15 and 16 are respectively a pair of excitation electrodes. 17 is a base board. 18, 19, and 20 are respectively a lead wire. 21, 24, and 25 are respectively a supporting arm. And, 22 and 23 are respectively a slit which corresponds to notches 6 and 7 in FIGS. 1a and 1b.
Also in such a piezoelectric vibrator unit for two vibrator plates of prior art, the drawbacks and difficulties as stated in the foregoing with respect to a vibrator unit for single vibrator plate are common. Moreover, serious drawbacks as will be stated in the following are inevitable in such a vibrator unit for two vibrator plates of prior art.
The close positioning of vibrator plates causes an interference of vibrations which necessarily results in deterioration of attenuation characteristics particularly when such a vibrator unit is used for a piezoelectric filter. And, insertion of a metal plate in between the vibrator plates is desired so as to overcome this. However, it is substantially impossible to provide means for supporting, in between vibrator plates 11 and 12, such an electrically conductive metal plate in a perfectly insulated state against supporting arms 12 and 16. Further, for a piezoelectric vibrator unit for more than three vibrator plates of a structure similar to such as shown in FIGS. 2a and 2b, another difficulty is present. That is, however the foregoing secondary vacuum evaporation process for the vibrator plates positioned at both ends could well be effected even after the same have been mounted, it would be impossible to carry out such a secondary vacuum evaporation process on an intermediate vibrator plate. Therefore, every vibrator plate must be subjected, one by one, to such a secondary vacuum evaporation process when it has been mounted and prior to the next one being mounted. Such means for manufacturing piezoelectric vibrator units is naturally extremely troublesome and inefficient.